Roviello and Sierger, J. Poly. Sci., Polym. Let. Ed., 13. 455 (1975), teach polymeric substances which exhibit melt anisotropic phases with optical properties appearing very similar to conventional, monomeric thermotropic liquid crystals. Others have synthesized a variety of polymers from novel monomers capable of forming liquid crystalline structures. In turn, these polymers have been evaluated to characterize the unique chemical and mechanical properties of polymer fibers, films, and molded articles fabricated from them. These unique properties have been attributed to the rigid rod-like structure of the monomers which imparts a collinear geometry to the mesogenic polymer repeating groups. Increased thermal stability, higher stiffness (modulus), and improved chemical resistance are generally obtained from the close packing of these polymer units in this stable mesophase, or liquid crystalline form.
Unless these rigid rod polymers are modified structurally, they are generally insoluble, infusible (not melt processable) and otherwise intractable. For example, poly(hydroquinone terephthalate) and poly (hydroquinone trans-1,4-cyclohexanedicarboxylate) are nonmesomorphic rigid polyesters with decomposition temperatures above 500.degree. C. (See Aguilera and Luderwald, Makromol. Chem., 179, 2817 (1978) and Kricheldorf and Schwarz, Makromol. Chem., 188, 1281-1294 (1987)). Alteration of the polymer structure by copolymerization with a non linear or "kink inducing" monomer such as isophthalic acid and/or a "flexible spacer" like 1,10-decanediol has been found to depress the melting point. (See Ghadage, J. Appl. Poly. Sci., 37, 1579-1588). Further, Delvin and Ober, Polymer Bull., 20, 45-51 (1988) report that the solubility of the stiff polymer so modified can be significantly improved.
Many of these liquid crystalline polymers have found commercial application as fibers, films, and plastics. The improvements which this class of polymers provide include high strength and modulus down to -195.degree. C.; excellent oxygen and water barrier properties; non dripping; no nitrous oxides or cyanides upon burning; dimensional stability up to 200.degree.-300.degree. C.; coefficient of thermal expansion equal to glass; transparent to microwave radiation; humidity resistance of 200 h at 120.degree. C. with no effect; very low moisture absorption; dielectric properties as good as high performance plastics; excellent stain resistance; low or no odor; and higher filler loading ability.